On Wed, Jul 02, 2014 at 03:32:59PM +0200, Joerg Roedel wrote:
> Hi David,
>
> On Wed, Apr 30, 2014 at 11:49:33AM +0100, David Woodhouse wrote:
> > There could be all kinds of existing mappings in the DMA page tables,
> > and I'm not sure it's safe to preserve them. What prevents the crashdump
> > kernel from trying to use any of the physical pages which are
> > accessible, and which could thus be corrupted by stray DMA?
> >
> > In fact, the old kernel could even have set up 1:1 passthrough mappings
> > for some devices, which would then be able to DMA *anywhere*. Surely we
> > need to prevent that?
>
> Ideally we would prevent that, yes. But the problem is that a failed DMA
> transaction might put the device into an unrecoverable state. Usually
> any in-flight DMA transactions should only target buffers set up by the
> previous kernel and not corrupt any data.
>
> > After the last round of this patchset, we discussed a potential
> > improvement where you point every virtual bus address at the *same*
> > physical scratch page.
>
> That is a solution to prevent the in-flight DMA failures. But what
> happens when there is some in-flight DMA to a disk to write some inodes
> or a new superblock. Then this scratch address-space may cause
> filesystem corruption at worst.
>
> So with this in mind I would prefer initially taking over the
> page-tables from the old kernel before the device drivers re-initialize
> the devices.
>
>
> Joerg
David, Joerg,
What do you think here? Do you want me to update the patch set for 3.17?
Jerry
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Jerry Hoemann Software Engineer Hewlett-Packard
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